1. Field of the Invention
The present invention relates to a recording/reproducing separated type magnetic head for use in magnetic disk apparatuses.
2. Description of the Prior Art
Along with the capacity enlargement of magnetic disk apparatuses, the requirement for higher recording density is increasing year after year. The apparatuses are also required to be smaller. To meet these requirements, state-of-the-art magnetic disk apparatuses use a giant magnetoresistive (GMR) head to perform the reproducing function of the recording/reproducing separated type magnetic head, with their recording track width being reduced to 0.3 μm and the gap between the head and the recording medium (hereinafter referred to as the flying height), to 13 nm, both approximately.
In order to achieve a high density of recording, the heads indispensably need to be lowered in flying height. However, along with the lowering of the flying height, the deformation of heads due to heat generation of coils in the inductive write thin film head during recording is posing an increasingly serious problem, because the deformation of heads would invite localized protrusion of the air bearing surfaces of the heads by about 3 nm and the consequent narrowing of the gap between the heads and the recording medium to about 10 nm, leading to possible collision of the heads and the recording medium, which would make head positioning impossible and in the worst case result in signal disappearance due to damaging of the recording medium or sliding of the heads. Studies on this problem include, for instance, what is reported in the IEEE Transactions on Magnetics, VOL. 38. NO.1, JANUARY 2002, pp 101.
FIG. 6 shows a schematic sectional view of a recording/reproducing separated type magnetic head using a GMR head. FIG. 7 and FIG. 8 respectively show thermal deformation of a head and how a head is worn by its contact with a recording medium. When heated, a head is deformed in such a way that its angled portion (the upper end of a protective film 13) protrudes forward with a substrate 1 as the base point. As a result, the protruding part of a multilayered protective film 19 on the air bearing surface comes into contact with the recording medium, and an area A is worn as shown in FIG. 8. The quantity of wear is defined by the width (w), height (h) and depth (d). According to the evaluation of a head whose flying height was approximately 0, the depth (d), width (w) and height (h) of the wear of the multilayered protective film 19 on the air bearing surface over an upper magnetic film 12 were 3 nm, 8 μm and 5 μm, respectively, at a recording frequency of 300 MHz, a write current of 50 mA and an ambient temperature of 60° C. even in a head improved in thermal protrusion (TPR) whose distance from the rear part of the upper magnetic film 12 to an air bearing surface shallow groove 14 was narrowed to 4 um or less as shown in FIG. 7. Thus, the wear of the multilayered protective film 19 on the air bearing surface over the upper magnetic film 12 due to the deformation of the head is too substantial to ignore. The wear depth of 3 nm accounts for 23% of the flying height of 13 nm between the head and the recording medium. This percentage corresponds to the 3.5-nm-thickness of the carbon film C of the multilayered protective film 19 on the air bearing surface.
A head can be deformed by differences among its constituent layers in the ratio of expansion when the head is heated. The heating of the head in turn would be due to its ambient temperature or its own heat generation. Among the factors of ambient temperature, the temperature within the magnetic disk apparatus is dominant. Many magnetic disk apparatuses are guaranteed against a temperature of about 60° C. The self-generated heat of the head mainly derives from Joule heating due to the electrification of coils at the time of writing, eddy current heating in the high frequency region, iron loss and an increase in resistance by the skin effect.
Deformation can be reduced by lowering the head temperature, the ambient temperature among various temperature elements is specified by the customer, and the manufacturer has to configure a structure that can meet the customer's requirement. On the other hand, to reduce the self-generated heat of heads, effective ways include reducing the resistance of coils, shaping the magnetic film compactly and using high-resistance magnetic materials. It is effective as well to reduce the volumic proportion of a material with a big difference in thermal expansion coefficient. More specifically, it is advisable to reduce the size of metallic films having a high thermal expansion coefficient, for instance, upper and lower shield films. Further, it is also effective to enhance the heat radiation effect. This can be achieved by providing a radiator plate near the source of heat. However, though the deformation of the head can be restrained to some extent by these means, deformation still occur as long as there are differences in thermal expansion coefficient among the constituent members, and it is impossible to completely eliminate contact between the head and the magnetic disk.